Magnetron oscillator



Jan. 7,1941. 5, UNDER 2,227,594

MAGNETRON OSCILLATOR Filed April 29, 1958 Summer Ernest GLinde-r Gttorneg Patented Jan. 7, 1941 UNITED STATES .22am monaraoiv osommroa Ernest G. hinder, Philafl Pa., casino:- to

Radio Corporation of America, a corporation of Delaware Application April 29, 1938, Serial No. 204,955

'Claims.

My invention relates to ultra high frequency oscillation generators, and more particularly to an effective multiple-anode magnetron of improved design in which the anodes are an inhera cnt part of a concentric line.

The increased efliciency at high frequencies of the four-anode magnetron, for example, as compared to the single or two-anode types is well established. It has been found that, as the fre- 1o quency of operation of a four-plate magnetron is increased, certain difficulties arise which more than offset the advantage of the four anodes. In fact. it has been found that at very high frequencies such magnetrons may become inoperall tlve. The diiiiculty referred to usuallylies in the fact that the interelectrode leads, which are commonly employed to connect opposite anodes, become resonant, or at least have appreciable inductance, and so destroy the oscillator efficiency.

I It is therefore an object of my invention to provide means for increasing the efllciency of an ultra high frequency magnetron oscillator.

A further object of my invention is to provide means whereby a multiple-anode magnetron cs- 25 cillator may be made more eflicient.

It is a further object of my invention to provide means in a magnetron oscillator for combinin: the features of resonant electrode oscillators and four-anode oscillators in a unique manner 30 which overcomes the difliculties encountered in interconnecting the anode sections.

This invention will be better understood from the following description when considered in connection with the accompanyin drawing. Its

to scope is indicated by the appended claims.

Referring to the drawing, Figure 1 is an example of the conventional type oi four-anode magnetron;

Figure 2 is a view, in. perspective, of the con- 40 struction of the cathode and anode elements of a magnetron according to this invention; and

Figure 3 is a connection diagram, partly in section, showing the circuit of a magnetron oscillator built according to this invention. gs Referring now to Fig. 1, a four-anode magnetron is shown connected in the well known manner to an oscillatory circuit 3. An example of a magnetron of this type is found in a U. S. patent to Posthumus, No. 2,103,638, issued De- 50 cember 28, 1937, and assigned to the assignee of this invention. It is to be noted that opposite anodes are connected together by conductors i and I, which extend around the outside of the plates. In practice, the actual connectors are u placed substantially as indicated in this diagram. The only practical way to reduce the length of the connectors is to reduce the overall diameter of the four anodes, because leads cannot be extended directly through the center of the tube without seriously affecting the perform- 5 ance of the oscillator. As the size of the anode electrodes is reduced, the ability to dissipate heat is also reduced. and therefore a practical limit is placed on such a change.

Referring to Fig. 2, a construction is shown which overcomes the diinculty of the connector lead inductance and permits the design of a tube which will handle large power without heating at frequencies higher than before obtainable. The anode electrode system comprises an outer metallic cylinder 9 and an inner metallic cylinder II. p The two cylinders are separated by a distance which is small in comparison to their diameters. The inner cylinder is axially divided into a number of arcuate sections so that the remainan ing surfaces are substantially equal to the spaces between them. For example, to obtain a fouranode magnetron a portion of the inner cylinder is bifurcated; that is, two opposite quadrants of one end of the inner cylinder are removed so that the end consists of two oppositely positioned arcuate surfaces I 3 and I5, which are a continuation of the inner cylindrical member ll, each subtending an angle of substantially 90.

The complete oscillator is shown in Fig. 3. go The overall length of the inner and outer cylinders is such that they form a concentric resonant line which is approximately a half wave length long. A voltage node will .exist at the mid-point of these electrodes, and therefore they may be conveniently positioned with respect to each other by means of a metallic annular collar II. This collar is the only contact between the two electrodes and is utilized to apply the D. C. voltage from a battery 3| to the electrodes. One or more "0 annular ceramic insulators it are placed within the inner cylinder to locate the cathode support member 20.

The outer cylinder 9 constitutes the envelope of the tube. Its two ends are sealed with glass end 5 bells l9, I9 through the former of which extends the coaxial cathode support member 20. The cathode 35 is a continuation of this support, and has its active portion only in the region limited by the bifurcated section of the inner cylinder I I. The axial length of the bifurcated section is largely determined by the heat dissipation requirement.

A small conductive spring It is used to maintain a uniform tension on the cathode as the I! 7 ing battery 28.

tubeexpands. Itissealedintheglassendbell ll at the cathode end oi. the tube. and provides one connection to the cathode. The cathode is heated by a battery 23, one end of which is grounded. A resistor 28 is provided with which to adjust the cathode current. A radio frequency choke 3! is connected between this resistor and the cathode support 2|. A second radio frequency choke 40 is connected between the conductive spring it and ground. A magnetic field is provided by a coil 21 and an energiz- The coil is placed around the electrodes II and I! in the manner shown.

Certain of the electrons attain a component of motion along the cathode axis. and therefore tend to travel out 01 the magnetic field. When this occurs they quickly lose their spiral motion and pass to the positive anode, It is desirable to regulate this action to prevent excessive anode current and to provide for optimum operating conditions. One eflective remedy is to extend the region oi! magnetic field axially -along the cathode. Another method is illustrated in Fig. 3. An end plate I is positioned within the inner cylinder near the inner end oi! the cathode 35. This end plate is supported by-the cathode support member 20, and insulated therefrom. A potential is applied to the end plate by a connection extending from the tube through an insulating head to a battery 43. The polarity or this potential is determined by'the tube geometry and the extent or the magnetic field. It is to be adjusted for optimum operating conditions;

When the magnetic field is applied, and the cathode energized, electrons are liberated from the cathode and, due to the force oi. the magnetic field, they rotate about the cathode and therefore approach the inner and outer anode electrodes alternately. The cut-away alternate quarters of the inner cylinder expose the outer cylinder to the electrons. Since oppositely positioned anode electrodes are connected together, the device will generate oscillations in the manner or the oscillator of Fig. 1. The inner and outer cylinders, including the anode electrodes l3 and I5, constitute a resonant tank circuit. The anode connecting leads which become resonant have been eliminated, and therefore greater efliciency may be obtained at ultra high frequencies. A load circuit 33 may be connected through suitable insulators to appropriate points on either side of the voltage node of the inner cylinder.

I claim as my invention: 1. An electronic device comprising an electron tube having an electron-emissive cathode, a resonant oscillatory circuit, and means for produc-' ing a magnetic field, said resonant oscillatory circuit comprising an inner and an outer cylinder concentrically positioned with respect to said cathode, said inner cylinder having an axially divided end portion the extensions oi which form a pair of symmetrically positioned anode sections, and the portion oi! said outer cylinder adjacent the openings between said inner cylinder anode sections forming an intermediate pair or anode sections.

2. An electronic device comprising an electron tube having a electron-emisslve cathode, a resonant oscillatory circuit, and means for producing a magnetic field, said resonant oscillatory circuit comprising an inner and an outer cylinder separatedbyadistancesmallincomparisontotheirao diameter and concentrically positioned with respect to said cathode, said inner cylinder having an axially divided end portion the extensions of which form a pair oi oppositely positioned anode sections. the portion of said outer cylinder adas jacent the openings between said inner cylinder jacent the openings between said inner cylinder anode sections forming other anode sections.

4. A device of the character described in claim 3 in which said inner cylinder is electrically connected to and supported by said outer cylinder at, a

a radio irequency voltage node.

5. A device or the character of claim 3 which inoluda an end plate electrode within said inner cylinder.

ERNEST G. LINDER. 5Q 

